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Found Looking for Machinests in Turning Aluminum

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REK

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I didn’t know where to post this, but I hope the watering hole is okay, if not the moderators can move it to somewhere appropriate.

I am looking for machinests who are experienced in turning down aluminum tubing. I need precison turned aluminum tubing to use as mandrels. They have to be within a 0.002” tolerance.

The length at 72” and wall at 1/4” or 1/8”. If need be, I can order the tubing as I know where to get it for cheap. This is going to be 6061 aluminum.
 
$$$$$$$$$
I am curious on what response you get. That's a pretty tight tolerance for a long wet noodle.
 
Have you considered ground hydraulic piston and/or ground precision oilfield rod?

NOTE: I'm not saying it'll work, it just seemed feasible on the surface when I looked at it and put it on the "not now" pile
 
Have you considered ground hydraulic piston and/or ground precision oilfield rod?

NOTE: I'm not saying it'll work, it just seemed feasible on the surface when I looked at it and put it on the "not now" pile

It will work, but they are extremely heavy. The last thing I need is to be sent to the hospital with a broken back lol.
 
Are you going doing room temperature cures or are you putting them in an oven? The thermal expansion alone is likely greater by a factor of two or three than the tolerance you're asking for.

Why does your tolerance "have" to be 0.002? Because it sounds cool? I'm not a machinist, but I am an aerospace engineer in the business of making really expensive composite parts for commercial and defense applications and I can tell you, 0.002 is a bit...sporty. It's not unheard of, but it's certainly not in the realm of "normal" in most aerospace applications. Tooling companies add a lot of zeros to tooling when you ask for that kind of precision. We use multi-million dollar Invar tools for some of our products and they're not that tight.
 
Refining and defining your tolerances will yield better response. Or, taking an approach of searching for a machinist who is set up for turning lengths of tubing, and then ask them what they can do. If their tooling is good, and they are skilled, they can probably do what you need. In thinking of all of the places that a tolerance of 0.002" could be applied, some are realistic, some are highly unlikely. Is that plus 0.002" or minus .002" or +/-.002"? and where? Sounds like some more research into learning what your needs really are, and how to ask for it is the next step. Good luck.
 
I didn’t know where to post this, but I hope the watering hole is okay, if not the moderators can move it to somewhere appropriate.

I am looking for machinests who are experienced in turning down aluminum tubing. I need precison turned aluminum tubing to use as mandrels. They have to be within a 0.002” tolerance.

The length at 72” and wall at 1/4” or 1/8”. If need be, I can order the tubing as I know where to get it for cheap. This is going to be 6061 aluminum.

I would love to give you a quote. first what is the final finished diameter, second what kind of finish are you wanting.the second question will mean a lot to the price, along with a realistic tolerance.
Thanks Gary
 
I would love to give you a quote. first what is the final finished diameter, second what kind of finish are you wanting.the second question will mean a lot to the price, along with a realistic tolerance.
Thanks Gary

How close of a tolerance can you get? The annoying part about aluminum is its high thermal expansion compared to other metals, makes it have the need for some tolerance.

I am looking for a 2.998” 3.498” and a 54mm at 2.148”. Let me know if this is do-able. I am not too crazy about the finish being polished or anything so no finish.
 
Are you going doing room temperature cures or are you putting them in an oven? The thermal expansion alone is likely greater by a factor of two or three than the tolerance you're asking for.

Why does your tolerance "have" to be 0.002? Because it sounds cool? I'm not a machinist, but I am an aerospace engineer in the business of making really expensive composite parts for commercial and defense applications and I can tell you, 0.002 is a bit...sporty. It's not unheard of, but it's certainly not in the realm of "normal" in most aerospace applications. Tooling companies add a lot of zeros to tooling when you ask for that kind of precision. We use multi-million dollar Invar tools for some of our products and they're not that tight.

It is going in an oven. By saying it has to have a 0.002” tolerance, is due to the nature of how a tube is turned down on a lathe. Even machines are not perfect and so there can be a taper on one end. That taper needs to be very little or else the cured composite tube can be stuck. I don’t know why you imply that it sounds cool, but let me assure you that it is not, because if I don’t have a good tolerance I can kiss the cured composite tube and the expensive mandrel goodbye.
 
0.002" is only 50um. That's not a particularly tight tolerance to get. Although confounding that is the fact it is aluminium and long, as others' have stated.

We have some parts machined to around 5um tolerance, but they are the stainless rods in the quadrupole of our mass spectrometer.
 
Also at what temperature are you wanting your toleranced dimension? Seeing as how you’re oven curing these does it need to cure at this dimension? So at heated temperatures?
 
How about machining the cured tube to size rather than the mandrel? If you get it within a few thou then you can ream it (or bore it?) to the final dimension without removing too much material. And you eliminate the thermal expansion variable coming into play.
 
My 2 cents .... I think you'd be better off having the tubing centerless ground. Not sure what it would cost. Turning something that long to that tolerance will not be easy.
This is your answer. look for centerless grinding or bar grinding in your area
 
You're probably best off sourcing DOM tubing in those dimensions. Seeing as they're common rocketry dimensions (aside from the 3.5"), odds are ALCOA is already making them or an email to Gary at AG71 machining ([email protected]) MAY turn up what you need, assuming he has material left.

Ask yourself if you truly need that tight of tolerance. In hobby rocketry, the answer is likely a resounding "NO."
 
I agree with what others have stated that you should be looking for someone to centerless grind these tubes for you.
 
54mm tubing even at 36 inches is a real pain to lathe
good luck in your quest
 
I've seen video of some machinists that can get those tolerances on steel over an 8ft long, 4in diameter solid shaft but not in 6061 Al hollow tubing. You could find someone with a tool post grinder that might be able to come close.
 
I have made mandrels to those tolerances, but not from hollow tubing. My suggestion is to make it from solid aluminum with a slight overall taper, whatever you can tolerate in the final ID spec of the composite tube. The surface finish is also important to allow breaking the mold release bond.

Another suggestion is to make the mandrel as two 36" pieces center-pinned together. The taper would be in both direction from the center (low at center, high at each end). Thread each end to crank in opposite direction to turn and pull the two-piece mandrel from both ends. The other advantage of two 36" pieces is that you'll find more people will lathes that can handle that length.
 
You probably dont need that kind of absolute accuracy on the size what you need is a variance of +-.002. If the size is off 50 microns its not a problem as long as the diameter is consistent.
 
I have made mandrels to those tolerances, but not from hollow tubing. My suggestion is to make it from solid aluminum with a slight overall taper, whatever you can tolerate in the final ID spec of the composite tube. The surface finish is also important to allow breaking the mold release bond.

Another suggestion is to make the mandrel as two 36" pieces center-pinned together. The taper would be in both direction from the center (low at center, high at each end). Thread each end to crank in opposite direction to turn and pull the two-piece mandrel from both ends. The other advantage of two 36" pieces is that you'll find more people will lathes that can handle that length.

As a user of Mandrels in a filament winding machine, I appreciate the original poster’s request - very hard to get off if the tolerances vary too much.

I really like John’s idea above. May give it a whirl.

I've also used 3d printed mandrels - if you print using HIPs filament, you can just dissolve the mandrel post cure in D-limonene.
 
First of all, my apologies, but I am unable to meet your request. I am not allowed to manufacture parts for sale on school machines.

However, as someone who has machined aluminum for this same purpose, I can say I have serious doubts that this would work, especially with the tubing you supply. My experiments with 4" inch OD tubing (0.125 wall) went poorly. There was noticeable warping after just two curing cycles.

If the parts are going into a curing oven, unless you use solid, stress-relieved aluminum rod (which is rather expensive), the mandrel is most likely going to warp way out of tolerance and soon become unusable.

For you, I believe the real challenge will be to find someone with the equipment necessarily to machine something 72 inches long. Since we do all of our machining in house, I don't really know who to approach.

I really like the tube I purchased from you and wish you luck with your business.
 
I have gotten quotes from eMachineShop before; you can submit a STEP file online.
https://www.emachineshop.com/

I spent about $5000 for a 50" long, 5" diameter Al mandrel back in 2000, so that's probably not relevant any longer. Widespread CnC machining should bring that price down quite a bit, but the length you're asking for will reduce the ease of making it.

Note that if the mandrel is not tapered, you will have a very hard time getting the part off (at least the first part or two until the mandrel is seasoned). I had to pack in the inside of the tube with dry ice for hours then pound from the end to get the first part off.

poundingmandrel.jpg


jcrocket.com/nike-asp.shtml#tubes
 
First of all, my apologies, but I am unable to meet your request. I am not allowed to manufacture parts for sale on school machines.

However, as someone who has machined aluminum for this same purpose, I can say I have serious doubts that this would work, especially with the tubing you supply. My experiments with 4" inch OD tubing (0.125 wall) went poorly. There was noticeable warping after just two curing cycles.

If the parts are going into a curing oven, unless you use solid, stress-relieved aluminum rod (which is rather expensive), the mandrel is most likely going to warp way out of tolerance and soon become unusable.

For you, I believe the real challenge will be to find someone with the equipment necessarily to machine something 72 inches long. Since we do all of our machining in house, I don't really know who to approach.

I really like the tube I purchased from you and wish you luck with your business.

Thanks Rocket501,

I’m curious what temperature did you heat it to? I never had an issue with warping thus far. Even with 1/16” walled aluminum tubing.

Also do you happen to know what type of aluminum was it? I know some metals down work so well with heat at low temperatures.
 
I have gotten quotes from eMachineShop before; you can submit a STEP file online.
https://www.emachineshop.com/

I spent about $5000 for a 50" long, 5" diameter Al mandrel back in 2000, so that's probably not relevant any longer. Widespread CnC machining should bring that price down quite a bit, but the length you're asking for will reduce the ease of making it.

Note that if the mandrel is not tapered, you will have a very hard time getting the part off (at least the first part or two until the mandrel is seasoned). I had to pack in the inside of the tube with dry ice for hours then pound from the end to get the first part off.

poundingmandrel.jpg


jcrocket.com/nike-asp.shtml#tubes

$5,000 ouch, I for sure will not pay that price. I will be sure to have it tapered, I was told it is better that way and I can see why.

Thank you John
 
Thanks Rocket501,

I’m curious what temperature did you heat it to? I never had an issue with warping thus far. Even with 1/16” walled aluminum tubing.

Also do you happen to know what type of aluminum was it? I know some metals down work so well with heat at low temperatures.

We cured the tubes at a maximum temperature of 300 degrees Fahrenheit for three hours.The alloy used was 6061 T6 aluminum. There wasn't all that much warping, but it was enough to prove troublesome.
 
We cured the tubes at a maximum temperature of 300 degrees Fahrenheit for three hours.The alloy used was 6061 T6 aluminum. There wasn't all that much warping, but it was enough to prove troublesome.

Ouch, yeah I never liked having a cure shedule of more than an hour. I mostly cure mine at 180F or 200F for an hour and that is it.

It is enough for the mandrel to expand and for the resin to cure rock solid. Once cooled the tubing would slip out.

I had issues in the past due to the short pot life of most resin systems. The resin would become solid first, before the aluminum could expand. This caused a tight grip around the mandrel and I could not remove it without the aid of a pick up truck to yank it out. The result ended up damaging my mandrels.
 
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